Leeds Study Uses Vinegar to Treat Chromium in Water

Engineers and environmental scientists at the University of Leeds are developing methods of helping contaminated water to clean itself by adding simple organic chemicals such as vinegar.

The harmful chromium compounds found in the groundwater at sites receiving waste from former textiles factories, smelters, and tanneries have been linked to cancer, and excessive exposure can lead to problems with the kidneys, liver, lungs, and skin, according to a March 3 press release from the university.

The research team, led by Doug Stewart, Ph.D., from the School of Civil Engineering and Ian Burke, Ph.D., from the School of Earth and Environment, has discovered that adding dilute acetic acid (vinegar) to the affected site stimulates the growth of naturally occurring bacteria by providing an attractive food source. In turn, these bacteria then cleanse the affected area by altering the chemical make-up of the chromium compounds to make them harmless.

"The original industrial processes changed these chemicals to become soluble, which means they can easily leach into the groundwater and make it unsafe," said Burke. "Our treatment method reconverts the oxidized chromate to a non-soluble state, which means it can be left safely in the ground without risk to the environment. As it is no longer 'bio-available' it doesn't present any risk to the surrounding ecosystem."

Chromate chemicals have previously been successfully treated in situ in neutral ph conditions, but this study is unique in that it concentrates on extremely alkaline conditions, which are potentially much more difficult to treat.

The current method of dealing with such groundwater contaminants is to remove the soil to landfill, which can be costly, both financially and in terms of energy usage. The Leeds methods being developed will allow treatment to take place on site.

Stewart said: "Highly alkaline chromium-related contaminants were placed in inadequate landfill sites in the UK right up until production stopped in the 1970s -- and in some countries production of large quantities of these chemicals still continues today. The soluble and toxic byproducts from this waste can spread into groundwater, and ultimately into local rivers, and therefore will remain a risk to the environment as long as they are untreated."

Current environmental regulations mean that before the team can test its research findings in the field, it needs water-tight proof that its methods can work, as it is illegal to introduce any substance into groundwater -- even where it is contaminated -- unless it has been shown to be beneficial.

"From the results we have so far I am certain that we can develop a viable treatment for former industrial sites where chromate compounds are a problem," said Stewart. "Our next step is to further our understanding of the range of alkalinity over which our system can operate. As society becomes more environmentally aware, new regulations demand that past mistakes are rectified and carbon footprints are reduced. By designing a clean-up method that promotes the growth of naturally occurring bacteria without introducing or engineering new bacteria, we are effectively hitting every environmental target possible."

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